Cytochalasin B (CB) is a mold metabolite which prevents cytoplasmic division without directly affecting nuclear division. CB appears to be a probe since it allows us to "dissect" out nuclear division and analyze its control in transformed cells. Experiments will utilize CB to show if all neoplastic cells show continued DNA synthesis and nuclear division (uncontrolled nuclear division, UND). It already has been shown that normal cells show marked inhibition of DNA synthesis and nuclear division in CB medium. UND will also be analyzed as a step, perhaps one of the final steps in a putative stepwise process of neoplasia. Factors inducing UND in vivo will be identified with the use of Millipore Filter Chambers. The mechanisms producing UND in malignant and DNA virus transformed cells will be identified by a number of experimental approaches. These include somatic cell hybridization, cell lines temperature sensitive for the transformed phenotype and the effects of proteases and cyclic nucleotides.